External Additive for Toner and Toner

The present disclosure relates to an external additive for toner and a toner.

In recent years, electrophotographic full-color copiers have become widely used and are beginning to be applied to the printing market. In the printing market, along with the increase in speed, there are growing demands for high image quality and high stability.

In order to increase the image quality and stability, the charging characteristics of the toner need to be stabilized. External additives have been variously investigated for stabilizing the charging characteristics of toners.

As an external additive to be used in toners, silica is generally widely known hitherto. Examples of silica with enhanced hydrophobicity by surface treatment of silica generally obtained by dry or wet (sol-gel) method have been reported. For example, Japanese Patent Laid-Open No. 2007-99582 discloses an example of a toner with improved charge stability by adding a highly hydrophobic spherical sol-gel silica microparticle to a toner particle (toner base particle).

Japanese Patent No. 6116711 discloses an example of a toner with improved flowability and charge stability by adding a polyalkyl silsesquioxane microparticle to a toner base particle.

However, the rising speed of initial charging of a toner is low under a high humidity environment, and when images are continuously output, the density variation or color variation of the images may become large.

The present disclosure provides an external additive for toner and a toner that solve the above disadvantages. Specifically, charging of a toner is risen rapidly even when an image is output under a high humidity environment, and also an image having charge stability and having suppressed density variation and color variation can be obtained.

The present disclosure provides an external additive for toner comprising an organosilicon polymer having a siloxane bond. In the external additive for toner, in X-ray photoelectron spectroscopic measurement, when the atomic concentration of silicon atoms is dSi, the atomic concentration of oxygen atoms is dO, the atomic concentration of carbon atoms is dC, and the sum thereof is 100 atom %, the proportion of the atomic concentration of carbon atoms bonding to silicon atoms is 30 atom % or more and 60 atom % or less; the silanol group amount measured by titration using KOH is 0.025 mmol/g or more and 0.800 mmol/g or less; and regarding silicon atoms contained in the organosilicon polymer, when the number of all silicon atoms is 1.00, the proportion of silicon atoms indicated by Siin the structure represented by the unit (a) below is Pa, the proportion of silicon atoms indicated by Siin the structure represented by the unit (b) below is Pb, and the proportion of silicon atoms indicated by Siin the structure represented by the unit (c) below is Pc, the Pa, the Pb, and the Pc satisfy the following expressions (1) and (2):

(Rand Reach independently represent an alkyl group having 1 or more and 6 or less carbon atoms).

The present disclosure relates to a toner including a toner particle and an external additive, and the external additive has the above structure.

Further features of the present disclosure will become apparent from the following description of exemplary embodiments.

In the present disclosure, the expression “xx or more and yy or less” or “xx to yy” indicating a numerical range means a numerical range including the lower limit and the upper limit as the endpoints, unless otherwise specified.

The present inventors believe that the mechanism expressing the effects of the present disclosure is as follows.

Silica particles and polyalkyl silsesquioxane particles, which have been used as external additives for toner, are particles of which the main component is a siloxane bond (Si—O—Si). Since the silica particle and the polyalkyl silsesquioxane particle have silanol groups at the ends thereof, unreacted residual silanol groups are present in the particle surface and the inside. Since a silanol group is prone to adsorb water, the charge amount of the toner decreases under a high humidity environment.

Against the above, the chargeability under a high humidity environment has been improved by trimethylsilylation (surface treatment) of the residual silanol group through coupling reaction by a silane compound or the like.

At the same time, it was demonstrated that the charge rising of a toner is highly affected by charging due to ion transfer of hydroxy groups and that the charge rising of the external additive with less silanol groups surface-treated as described above slows down.

The present inventors have conducted extensive research and, as a result, found that the above disadvantages can be solved by optimizing the proportion of the atomic concentration of carbon atoms bonding to silicon atoms in an organosilicon polymer and the silanol group amount, and arrived at the present disclosure.

The present disclosure provides an external additive for toner, comprising an organosilicon polymer having a siloxane bond. In the external additive for toner, in X-ray photoelectron spectroscopic measurement, when the atomic concentration of silicon atoms is dSi, the atomic concentration of oxygen atoms is dO, the atomic concentration of carbon atoms is dC, and the sum thereof is 100 atom %, the proportion of the atomic concentration of carbon atoms bonding to silicon atoms is 30 atom % or more and 60 atom % or less; the silanol group amount measured by titration using KOH is 0.025 mmol/g or more and 0.800 mmol/g or less; and regarding silicon atoms contained in the organosilicon polymer, when the number of all silicon atoms is 1.00, the proportion of silicon atoms indicated by Siin the structure represented by the unit (a) below is Pa, the proportion of silicon atoms indicated by Siin the structure represented by the unit (b) below is Pb, and the proportion of silicon atoms indicated by Siin the structure represented by the unit (c) below is Pc, the Pa, the Pb, and the Pc satisfy the following expressions (1) and (2):

(Rand Reach independently represent an alkyl group having 1 or more and 6 or less carbon atoms).

Firstly, in the external additive for toner of the present disclosure, in X-ray photoelectron spectroscopic measurement, when the atomic concentration of silicon atoms is dSi, the atomic concentration of oxygen atoms is dO, the atomic concentration of carbon atoms is dC, and the sum thereof is 100 atom %, the proportion of atomic concentration of carbon atoms bonding to silicon atoms is 30 atom % or more and 60 atom % or less.

In the above-mentioned range, the rising of toner charging is improved, and the durable stability is excellent. Accordingly, the concentration stability and color stability of images are improved. When the proportion of atomic concentration of carbon atoms is less than 30 atom %, since the hydrophobicity is insufficient, the charge rising speed under a high humidity environment decreases. When the proportion of atomic concentration of carbon atoms is greater than 60 atom %, since the mechanical strength of the particle decreases, collapse of the external additive occurs, and the charge stability of the toner decreases.

The proportion of the atomic concentration of carbon atoms in the external additive for toner can be controlled by the mixing ratio of an alkoxysilane having the above structure and the type and addition amount of the surface treatment agent. For example, when the proportion of the atomic concentration of carbon atoms is required to decrease, for example, the mixing ratio of the alkoxysilane having the above structure (a) is increased, the mixing ratio of the alkoxysilane having the above structure (b) or (c) is decreased, or the addition amount of the surface treatment agent is decreased. When the proportion of the atomic concentration of carbon atoms is required to increase, for example, the mixing ratio of the alkoxysilane having the above structure (a) is decreased, the mixing ratio of the alkoxysilane having the above structure (b) or (c) is increased, or the addition amount of the surface treatment agent is increased. The proportion of the atomic concentration of carbon atoms in the external additive for toner can be 30 atom % or more and 40 atom % or less.

Secondly, in the external additive for toner of the present disclosure, the silanol group amount measured by titration using KOH is 0.025 mmol/g or more and 0.800 mmol/g or less. When the silanol group amount is within the above range, the charge rising speed of the toner under a high humidity environment can be increased. Accordingly, the initial charge stability can be improved, and the concentration and color variations of images can be suppressed.

The silanol group amount of the external additive for toner can be controlled by the mixing ratio of the alkoxysilane having the above structure, the temperature and time periods of the hydrolysis process and the condensation process, the type and addition amount of the surface treatment agent, and the treatment conditions. For example, when the silanol group amount is required to increase, for example, the mixing ratio of the alkoxysilane having the above structure (a) is increased, the mixing ratio of the alkoxysilane having the above structure (b) or (c) is decreased, the temperature of the hydrolysis and condensation processes is increased, or the time periods of the hydrolysis and condensation processes are increased. When the silanol group amount is required to decrease, for example, the mixing ratio of the alkoxysilane having the above structure (a) is decreased, the mixing ratio of the alkoxysilane having the above structure (b) or (c) is increased, the temperature of the hydrolysis and condensation processes is decreased, or the time periods of the hydrolysis and condensation processes are decreased.

Furthermore, regarding silicon atoms contained in the organosilicon polymer included in the external additive for toner of the present disclosure, when the number of all silicon atoms is 1.00, the proportion of silicon atoms indicated by Siin the structure represented by the above unit (a) is Pa, the proportion of silicon atoms indicated by Siin the structure represented by the above unit (b) is Pb, and the proportion of silicon atoms indicated by Siin the structure represented by the above unit (c) is Pc, the Pa, the Pb, and the Pc satisfy the following expressions (1) and (2):

Within the above range, when the toner is subjected to stress from a member such as a carrier, the external additive itself is hardly broken, and, furthermore, the external additive can be prevented from being embedded in the toner particle surface because of its appropriate flexibility. Consequently, the toner surface condition hardly changes, and the chargeability and adhesion of the toner can be more suppressed from changing. The content rates of the above units (a), (b), and (c) in the external additive can be controlled by the addition amount of the alkoxysilane having the above structure.

The method for manufacturing the external additive for toner of the present disclosure is not particularly limited, but the particles may be formed through hydrolysis and condensation polymerization reactions of a silicon compound (silane monomer) by a sol-gel method. Specifically, a mixture of a difunctional silane having two siloxane bonds and a tetrafunctional silane having four siloxane bonds is hydrolyzed and condensation-polymerized, and colloidal silica or the like is reacted therewith to form a composite particle. Silane monomers such as the difunctional silane and the tetrafunctional silane and the composite particle will be described later. The proportion of the difunctional silane is preferably 30 mol % or more and 70 mol % or less and more preferably 40 mol % or more and 60 mol % or less. The proportion of the tetrafunctional silane is preferably 30 mol % or more and 80 mol % or less and more preferably 40 mol % or more and 70 mol % or less.

The external additive for toner of the present disclosure is a particle containing an organosilicon polymer having a siloxane bond.

The method for manufacturing the organosilicon polymer is not particularly limited, and the organosilicon polymer can be obtained by, for example, dropwise adding a silane compound to water, performing hydrolysis and condensation reactions by a catalyst, and then filtrating and drying the obtained suspension. The particle diameter can be controlled by the type of the catalyst, the mixing ratio, the reaction starting temperature, the time period of dropping, and so on. Examples of the catalyst include, but not limited to, acidic catalysts such as hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid; and basic catalysts such as aqueous ammonia, sodium hydroxide, and potassium hydroxide.

The external additive for toner including the organosilicon polymer can be manufactured by the following method.

Specifically, the method can include a first process of obtaining a hydrolysate of a silicon compound, a second process of mixing the hydrolysate and an alkaline aqueous medium for polycondensation reaction of the hydrolysate, and a third process of mixing the polycondensation reaction product and an aqueous solution for particleization. In some cases, in the third process, a hydrophobizing agent may be further mixed. In the second process, an inorganic microparticle such as colloidal silica or a resin microparticle may be used. Although the details will be described later, these microparticles are the microparticle B in the composite particle.

In the first process, a silicon compound and a catalyst are brought into contact with each other by a method such as stirring or mixing in an aqueous solution prepared by dissolving an acidic or alkaline material that functions as the catalyst in water. As the catalyst, a known catalyst can be suitably used. Specifically, examples of the catalyst include acidic catalysts such as acetic acid, hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid; and basic catalysts such as aqueous ammonia, sodium hydroxide, and potassium hydroxide.

The use amount of the catalyst may be appropriately controlled depending on the types of the silicon compound and catalyst. For example, the use amount can be selected within a range of 1×10parts by mass or more and 1 part by mass or less based on 100 parts by mass of water used for hydrolyzing the silicon compound.

When the use amount of the catalyst is 1×10parts by mass or more, the reaction proceeds satisfactorily. In contrast, when the use amount of the catalyst is 1 part by mass or less, the amount of the catalyst remaining as an impurity in the microparticle is low, and hydrolysis easily proceeds. The use amount of water can be 2 mol or more and 15 mol or less based on 1 mol of the silicon compound. When the amount of water is 2 mol or more, the hydrolysis reaction proceeds satisfactorily, and when the amount is 15 mol or less, the productivity is improved.

The reaction temperature is not particularly limited, and the reaction may be performed at ordinary temperature or under heating conditions. However, the reaction may be performed while maintaining a temperature of 10° C. to 60° C., because the hydrolysate can be obtained in a short time and also partial condensation reaction of the generated hydrolysate can be suppressed. The reaction time is not particularly limited and may be appropriately selected considering the reactivity of the silicon compound to be used, the composition of a reaction solution prepared from the silicon compound, an acid, and water, and the productivity.

In a method for manufacturing a silicon polymer particle, as the second process, the raw material solution obtained in the first process and an alkaline aqueous medium are mixed to subject the particle precursor to polycondensation reaction. Consequently, a polycondensation reaction solution is obtained. Here, the alkaline aqueous medium is liquid obtained by mixing an alkaline component, water, and an organic solvent or the like as needed.

The alkaline component used in the alkaline aqueous medium is a component whose aqueous solution is basic and functions as a neutralizer for the catalyst used in the first process and functions as a catalyst for the polycondensation reaction in the second process. Examples of the alkaline component include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; ammonia; and organic amines such as monomethylamine and dimethylamine.

The use amount of the alkaline component is an amount allowing neutralization of the acid and functioning effectively as a catalyst for the polycondensation reaction. For example, when ammonia is used as the alkaline component, the amount is selected usually within a range of 0.01 parts by mass or more and 12.5 parts by mass or less based on 100 parts by mass of a mixture of water and an organic solvent.

In the second process, in order to prepare an alkaline aqueous medium, in addition to the alkaline component, an organic solvent may be further used. The organic solvent is not particularly limited as long as it has compatibility with water, but an organic solvent that dissolves 10 g or more of water per 100 g under ordinary temperature and normal pressure can be used.

Specifically, examples of the organic solvent include alcohol such as methanol, ethanol, n-propanol, 2-propanol, and butanol; polyhydric alcohol such as ethylene glycol, diethylene glycol, propylene glycol, glycerol, trimethylolpropane, and hexanetriol; ether such as ethylene glycol monoethyl ether, acetone, diethyl ether, tetrahydrofuran, and diacetone alcohol; and amide compounds such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

A mong the above-mentioned organic solvents, an alcoholic solvent such as methanol, ethanol, 2-propanol, and butanol may be used. Furthermore, from the viewpoint of hydrolysis and dehydration condensation reactions, the same alcohol as the alcohol generated by elimination can be selected as the organic solvent.

As the third process, the polycondensation reaction product obtained in the second process is mixed with an aqueous solution for particleization. As the aqueous solution, water (tap water, pure water, or the like) can be suitably used, and water may further contain a component having compatibility with water, such as a salt, an acid, an alkali, an organic solvent, a surfactant, and a water-soluble polymer. The temperature of the polycondensation reaction solution and the aqueous solution when mixed is not particularly limited and may be suitably selected within a range of 5° C. to 70° C. considering the compositions thereof, productivity, and so on.

As the method for collecting the particles, a known method can be used without particular limitation, and examples thereof include a method by scooping floating powder and a filtration method, and the filtration may be used because of its ease of use. The method of filtration is not particularly limited, and a known apparatus for vacuum filtration, centrifugal filtration, pressure filtration, or the like may be selected. The filter paper, filter, filter cloth, and so on that are used for the filtration are not particularly limited as long as it is available industrially and may be appropriately selected depending on the apparatus to be used.

The monomer to be used can be appropriately selected depending on the compatibility with the solvent and catalyst or hydrolyzability. Examples of the tetrafunctional silane monomer having the above structure (a) include tetramethoxysilane, tetraethoxysilane, and tetraisocyanatesilane. Among these monomers, tetraethoxysilane may be used.

Examples of the trifunctional silane monomer having the above structure (b) include methyltrimethoxysilane, methyltriethoxysilane, methyldiethoxymethoxysilane, methylethoxydimethoxysilane, methyltrichlorosilane, methylmethoxydichlorosilane, methylethoxydichlorosilane, methyldimethoxychlorosilane, methylmethoxyethoxychlorosilane, methyldiethoxychlorosilane, methyltriacetoxysilane, methyldiacetoxymethoxysilane, methyldiacetoxyethoxysilane, methylacetoxydimethoxysilane, methylacetoxymethoxyethoxysilane, methylacetoxydiethoxysilane, methyltrihydroxysilane, methylmethoxydihydroxysilane, methylethoxydihydroxysilane, methyldimethoxyhydroxysilane, methylethoxymethoxyhydroxysilane, methyldiethoxyhydroxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltrichlorosilane, ethyltriacetoxysilane, ethyltrihydroxysilane, propyltrimethoxysilane, propyltriethoxysilane, propyltrichlorosilane, propyltriacetoxysilane, propyltrihydroxysilane, butyltrimethoxysilane, butyltriethoxysilane, butyltrichlorosilane, butyltriacetoxysilane, butyltrihydroxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, hexyltrichlorosilane, hexyltriacetoxysilane, hexyltrihydroxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltrichlorosilane, phenyltriacetoxysilane, and phenyltrihydroxysilane. Among these monomers, methyltrimethoxysilane may be used.

Examples of the difunctional silane monomer having the above structure (c) include di-tert-butyldichlorosilane, di-tert-butyldimethoxysilane, di-tert-butyldiethoxysilane, dibutyldichlorosilane, dibutyldimethoxysilane, dibutyldiethoxysilane, dichlorodecylmethylsilane, dimethoxydecylmethylsilane, diethoxydecylmethylsilane, dichlorodimethylsilane, dimethoxydimethylsilane, diethoxydimethylsilane, and diethyldimethoxysilane. In particular, dimethyldimethoxysilane may be used. Physical properties and forms of external additive for toner

The primary particle of the external additive for toner of the present disclosure can have a number-average diameter of 0.03 μm or more and 0.30 μm or less. When the primary particle has a number-average diameter within the above range, microparticles can be uniformly coated on the toner particles. In addition, since the stress to the toner can be suppressed, the effect of charge stability can be easily obtained. When the primary particle of the microparticle has a number-average diameter of less than 0.03 μm, since the stress to the toner is increased when a large amount of images with low printing density is output over a long period of time, the external additive particle may be easily embedded in the toner surface. When the primary particle has a number-average diameter of greater than 0.30 μm, the external additive particle may be easily eliminated from the toner surface. The number average particle diameter of the primary particle of the external additive can be increased by lowering the reaction temperature, decreasing the reaction time, or increasing the catalyst amount in the hydrolysis and condensation processes. The number average particle diameter of the primary particle of the microparticle can be decreased by raising the reaction temperature, elongating the reaction time, or decreasing the catalyst amount in the hydrolysis and condensation processes.